Brain changes during adolescence

- [Instructor] When we think about changes that happen during puberty, we usually think about changes that happen to the body. Things like the development of secondary sex characteristics or changes in height or an increase in body hair. But those aren't the only changes that happen. There are actually a lot of changes that happen to the brain as well. Here I have an image of a brain. This is what you would see if you looked at the side of the brain. Here is the front towards the face. Here's the back. And then over here, I have another brain and this brain is sliced in half. This brain is sliced right down the middle. These two brains are facing each other. So here's the front. And then here's the back of this one. One of the major changes that we see during adolescence is the development of the frontal lobe, particularly the prefrontal cortex. I'll roughly indicate where on the brain that is. This is the area of the brain that is responsible for what scientists call higher order cognition. Things like thinking about the future, and planning, and decision making. And also the ability to inhibit certain behaviors and focus on longterm goals. This part of the brain doesn't really stop maturing until our early twenties. Because it is still developing during the teenage years, because it isn't fully developed. this might help to explain why teenagers sometimes show poor judgment. Another area of the brain that continues to develop during adolescence is the limbic system. This includes a number of different brain structures. This image isn't really the best way to view them because a lot of the structures are on either side of the midline. Even so, I want to point out about where they are in the brain. One structure included in the limbic system is the amygdala, which would be about here. This is the part of our brain that's responsible for emotions and emotional responses. It also includes the hypothalamus, which is here and let me pick a slightly different color for that. This part of the brain regulates a surprising number of things. But in particular, I wanna focus on its role concerning the endocrine system or the hormone system in our bodies. To be clear, the limbic system includes a bunch of other structures as well, but I really wanna focus on these two, because in combination with the prefrontal cortex, which helps to regulate our emotions, the fact that these structures are still developing during the teenage years might help to explain why teenagers can sometimes be moody, why they might sometimes have emotional outbursts, like yelling at their parents and stomping out of the room and slamming the door. While I think that this is kind of funny and while it kind of makes me want to roll my eyes when teenagers act out, this does actually have some really important legal implications, like whether or not we should be able to charge teenagers like adults when they commit certain crimes. This is a question that I put to you. Should teenagers get the same treatment as adults if they commit the same crimes? Should they be able to be sentenced to death or to life in prison for acts that they commit prior to turning 18? Do you think that this is a good boundary? Are crimes committed one month before someone's 18th birthday really different from crimes that they commit one month after? Where should this boundary be? How should we define adulthood? These are really difficult and serious questions and it's really not clear what role developmental research has in solving these problems or if it should even have a role at all. Putting that very serious question aside, another area of the brain that changes during adolescence is the corpus callosum, which you can see here. This is the area of the brain that connects our left and right hemispheres. There are a number of things that change about the structure during adolescence. But in particular, I really wanna focus on the changes to connections that are associated with language and language learning. These connections grow before and during puberty but this growth stops soon afterwards. This might help to explain why learning a second language is so much easier in childhood as compared to adulthood. So we see changes to those specific brain areas but there are also other more global changes that are happening in the brain during this period or changes that are happening throughout the brain. One thing that we see during this period is an increase in myelination, especially in the areas that are associated with higher order functioning. To quickly review, this is a neuron and neurons communicate with each other by sending signals down these long axons. Myelin is a fatty tissue that covers the axons of neurons and helps to increase the speed at which the neurons can communicate. Faster communication between neurons means faster communication between brain areas. This can help explain why adolescents are able to process information faster than children. Another thing that we see during this time period is that there's an increase in brain volume during early adolescence and then this shrinks during late adolescence. This suggests that adolescence is a period of synaptic pruning or cutting weak connections in the brain. So this is your body literally breaking down connections between neurons. You might initially think that this is a bad thing, but this pruning is actually really good and it's really important because it allows the body to focus energy and resources on the connections that are used most. A kind of scary implication of this is that what we do during our teenage years might be literally shaping our brains for the rest of our lives. But there's kind of a use it or lose it principle at work here. So if we spend our free time reading, or playing sports, or focusing on academics, and having good time management skills, then that's what's going to be reinforced. The parts of the brain that are responsible for those behaviors are physically going to be strengthened. But if we spend most of our time watching TV and sitting on our couch and procrastinating, that's what's going to be strengthened instead.